Luckily stock rims won't dry your wallet.

http://mjbobbitt.home.comcast.net/~mjbobbitt/mustang/5lug.html
Try checking that website.
The author provides several clues to help you choose which rims to use.

Where do they rub exactly?

if they rub on the quad shocks in the rear you can try turning them around.

can't turn the quads around, I've got aftermarket ones that look like actual shocks. KYB or something like that. They rub up in the front, not too awfully bad, but bad enough for me to notice.

Do you know how to measure the backspacing of what you have now???

Lay a straight edge across the inner lip of the rim. Measure the distance from the mounting surface of the center to that staight edge. A stock 16" by 7" wide Pony wheel is just under 5 inches. About 4.8 inches. This sets the INNER spacing of the tire from the shocks and inner wheelwell walls.

If you use more back spacing, the tire moves closer to the shocks. If you use less, it moves out towards the outer fender lip.

If you use a wider rim for a certain amount of back spacing, the outer tire sidewall moves out. The amount it moves out from rim width is complex, and depends on the sidewall construction and tread width.

You could use a spacer if you don't mind the mounting being a little weaker.

Tom